tagged-json.js

//@ts-check

class PushbackIterator {
    /**
     * @param {Iterator<string, string, string>} stringIter
     */
    constructor(stringIter) {
        /** @type {Iterator<string, string, string>} */
        this.stringIter = stringIter;
        /** @type {Array<string>} */
        this.backBuffer = [];
    }

    /**
     * @param {string} char 
     */
    pushBack(char) {
        this.backBuffer.push(char);
    }

    next() {
        if (this.backBuffer.length) {
            return { value: this.backBuffer.pop(), done: false };
        } else {
            return this.stringIter.next();
        }
    }

    [Symbol.iterator]() {
        return this;
    }
}

/**
 * @param {PushbackIterator} stringIter
 * @param {string} stopChar
 * @returns {string}
 */

function copyString(stringIter, stopChar) {
    let result = "";
    for (const char of stringIter) {
        if (char === stopChar) break;
        result += char;
    }
    return result;
}

/**
 * @param {PushbackIterator} stringIter
 * @returns {string}
 */

function readName(stringIter) {
    let result = "";
    for (const char of stringIter) {
        if (!char.match(/[a-z0-9_]/i)) {
            stringIter.pushBack(char);
            break;
        } 
        result += char;
    }
    return result;
}

/**
 * @param {PushbackIterator} jsonString 
 * @param {string=} propertyName 
 * @param {string=} stopChar
 * @returns {string}
 */

function untag(jsonString, stopChar = "", propertyName = "type") {
    let result = "";

    for (const char of jsonString) {
        if (char === `"`) {
            result += `"${copyString(jsonString, `"`)}"`;
        } else if (char.match(/[a-z]/i)) {
            const name = char + readName(jsonString);
            result += copyString(jsonString, "{") + "{";
            result += (` "type": "${name}",` + untag(jsonString, "}", propertyName)).replace(/,\s*$/, " ");
            result += "}";
        } else if (char === stopChar) {
            return result;
        } else {
            result += char;
        }
    }

    return result;
}